A demonstration has taken place outside the US consulate in Hong Kong in support of American whistleblower Edward Snowden who is still believed to be in the region.

Ex-CIA worker Mr Snowden has not been seen since he left a hotel there last Monday where he had given a newspaper interview about a secret US internet surveillance programme.

Hundreds of supporters, backing his quest for freedom of speech and denouncing the programme, marched to the consulate where they delivered a letter addressed to Consul General Steve Young.

They also urged the city's government not to extradite Mr Snowden.

Demonstrators, including pro-democracy lawmakers, activists and a large number of expatriates, held banners and shouted "Defend Free Speech", "Protect Snowden", "No Extradition" and "Respect Hong Kong Law".

Many blew whistles and wore masks with Mr Snowden's face on it.

Sky's Mark Stone reporting from the scene said the protest had put China in a "relatively difficult position".

He said: "On one hand, China must be relishing in the fact that a US spy has admitted that the Americans have been spying on the Chinese.

"But on another hand, this protest is something the Chinese will not be very comfortable with - the idea that people are demonstrating for free speech in a territory which is Chinese."

Hong Kong has a long-standing extradition treaty with the US, but Beijing has the potential to veto any ruling.

Mr Snowden is still believed to be in Hong Kong

"Snowden is now in Hong Kong and falls under our jurisdiction and we have to defend the fact that the city's courts are in the position to deal with the situation," rally spokeswoman Oiwan Lam said.

The UK Government has urged airlines worldwide not to allow Mr Snowden to board flights to Britain.

The alert, dated Monday on a Home Office letterhead, said carriers should prevent the former US intelligence contractor boarding UK-bound flights because "the individual is highly likely to be refused entry to the UK".

Mr Snowden, 29, who worked for the National Security Agency (NSA), leaked top-secret information about the controversial US Prism programme.

He has admitted to giving details of the monitoring of phone calls and internet data from companies such as Google and Facebook, to The Guardian and Washington Post.

He said he is not trying to hide from justice in Hong Kong, where he fled to last month.

Snowden told the South China Morning Post newspaper he was "neither a traitor nor hero. I'm an American".

"People who think I made a mistake in picking Hong Kong as a location misunderstand my intentions," he said in an excerpt of the interview released by the paper.

"I am not here to hide from justice; I am here to reveal criminality."

Based on the information leaked by Mr Snowden, the publications disclosed the existence of the Prism system - set up by America's NSA to track customer data directly from ISP servers to fight the threat of terrorism.

The US has launched a criminal investigation to prosecute Mr Snowden for lifting the lid and exposing the classified material.